recovery of metals from deep eutectic solvents
TRANSCRIPT
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Recovery of metals from Deep Eutectic Solvents
Stylianos Spathariotis
This project has received funding from the European Union's EU Framework Programme for Research and Innovation Horizon 2020
under Grant Agreement No 721385https://etn-socrates.eu/
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Circular economy of metals
RedoxM Mx+
MYY = O, S, As, Te, Se etc
Thermodynamics of species stability depends on:
(Applied) potentialLigand type
and concentration
Metal concentrationTemperature,
Stirring
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SOCRATES project
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• Project aims to gain value from metallurgical residues
• My project is to extract and recover metals from waste using DESs
• Electrodeposition and cementation to reduce metal ions
https://www.youtube.com/watch?v=9ilrNeKG4D8
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Deep eutectic solvents
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HBDs are INEXPENSIVE (£1/kg)Non – toxicNon – flammableBiodegradableVersatile (>105)
Acids, Amides, Alcohols
Quaternary ammonium saltCholine chloride – vitamin in chicken feed
Hydrogen bond donorUrea – common fertiliser
Dissolution of salts, metal oxides, polar organics, amino acids, enzymes, surfactants
Ethaline 200
Choline chloride+
Ethylene glycolChem. Comm., 2003, 70JACS, 2004, 126, 9142Chem. Rev., 2014,114, 11060-82
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Electrodeposition
Cu
• Reversible metals can be electrowon easily with high current efficiency
• Non-reversible/oxophillic metals – deposition is very dependent on concentration, stirring and temperatureLow current efficiency due to film formation.
Pb Ag Sn
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Co
NiFe
Zn
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-1.5 -1.0 -0.5 0.0-6
-4
-2
0
2
J (
mA
/cm
2)
E (V) vs Ag/AgCl
25oC
80oC
Temperature Metal concentration
-1.5 -1.0 -0.5 0.0 0.5
-2
-1
0
1
2
3
4
J (
mA
/cm
2)
E (V) vs Ag/AgCl
0.3M
0.1M
0.05M
Stirring
-1.5 -1.0 -0.5 0.0-3
-2
-1
0
J (
mA
/cm
2)
E (V) vs Ag/AgCl
Unstirred
500 rpm
1000 rpm
Changing experimental parameters can make metals behave in a more reversible wayand increase deposition efficiency
Factors affecting metal deposition
Zn in Ethaline
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Metal in ethaline
E /V
Cu2+ + e- ⇌ Cu+ 0.39
Fe3+ + e- ⇌ Fe2+ 0.29
Ag+ + e- ⇌ Ag0 -0.15
Cu+ + e- ⇌ Cu0 -0.42
Fe2+ + 2e-⇌ Fe0 -0.59
Ni2+ + 2e- ⇌ Ni0 -0.62
Co2+ + 2e- ⇌ Co0 -0.64
Sn2+ + 2e-⇌ Sn0 -0.64
Pb2+ + 2e- ⇌ Pb0 -0.73
Zn2+ + 2e-⇌ Zn0 -1.12
Redox potentials
Cementation
Wide range of metals able to be cemented with sustained deposition
Zn
Zn2+
Mn+
M
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Cementation on Zn
0 2 4 6 8 10
0.01
0.02
0.03
0.04
0.05
Co
nce
ntr
atio
n (
M)
Time (h)
Fe
Co
Ni
Sn
Ag
Cu
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
0
5
10
15
20
k/ 1
00
s-1
E / V
Ag
Sn
Fe Cu
Ni
Co
PbCementation with Zn not driven solely by thermodynamicsPotentially side reactions occur e.g. passivation
Cementation is a pseudo first order process (diffusion controlled)Aqueous cementation → pH < 4 to prevent passivationDES cementation → neutral pH
Oxidation of Zn is so fast, it pits the surface and the reduced metal falls off the substrate as a powder.
Ag
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Cementation on Cu
Cementation works better on metals which do not passivate
Sa = 0.34 µm
Substrate Ag 5 mM
Sa= 0.45 µm
Sa= 0.50 µm
Ag 20 mM Ag 50 mM
Sa= 0.84 µm
CuCA
Separated cementation mechanism
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Metal recovery from Jarosite
Electrochemical dissolution of 500 g Jarosite at the anodeRecovered by electrowinning & cementation
Metal Removal (%)
Fe: 63 Pb: 71 Zn: 80
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Metal recovery from complex mixtures
Cementation
Initial atomic ratio 25 Fe : 1 Pb : 15 Zn
Ethaline + Oxalic acidFe : Zn : Pb
0.2 : 0.02 : 1
Electrodeposition
Ethaline + Oxalic acidFe : Pb
0 : 1
Complexing agents can enhance selectivity
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Conclusions
✓DESs can be used for metal deposition
✓ Electrodeposition and cementation are linked to reversibility
✓ Temperature, stirring and metal concentration affect deposition
✓ Efficiency of non reversible metals is low due to passivation
✓Complexing agents can enhance selectivity
✓Potentially useful for secondary metal recovery for high value elements e.g. PCBs
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Acknowledgments
• European Union
• Materials group
• Socrates group
This project has received funding from the European Union's EU Framework Programme for Research and Innovation
Horizon 2020 under Grant Agreement No 721385https://etn-socrates.eu/
Interested in my work? Contact me !